JP2011187234A - Nonaqueous electrolyte and nonaqueous electrolyte secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte for a nonaqueous electrolyte secondary battery enhancing initial efficiency and low temperature discharge characteristics, and suppressing the amount of gas generation after high temperature storage. <P>SOLUTION: A nonaqueous electrolyte contains a fluorine substitution ether represented by chemical formula (1), and a monofluorophosphate and/or a difluorophosphate. In the formula, Rf<SB>1</SB>represents a hydrogen atom, a fluorine atom, an alkyl group in which at least a part of hydrogen atoms is replaced by a fluorine atom, or an alkoxy alkyl group in which at least a part of hydrogen atoms is replaced by a fluorine atom; Rf<SB>2</SB>represents an alkyl group in which at least a part of hydrogen atoms other than one hydrogen atom bonded with a terminal carbon atom is replaced by a fluorine atom or an alkoxy alkyl group in which at least a part of hydrogen atoms may be replaced by a fluorine atom. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery using the same.

With the rapid progress of portable electronic devices such as mobile phones and notebook personal computers, there is an increasing demand for higher capacities for batteries used for the main power source and backup power source, such as nickel cadmium batteries and nickel Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries having a higher energy density than hydrogen batteries have attracted attention.
As an electrolyte for a lithium ion secondary battery, an electrolyte such as LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ (CF ₂ ) ₃ SO ₃ , or a high dielectric constant such as ethylene carbonate or propylene carbonate is used. A typical example is a non-aqueous electrolyte solution dissolved in a mixed solvent of a solvent and a low-viscosity solvent such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate.

  In addition, as a negative electrode active material of a lithium ion secondary battery, a carbonaceous material capable of occluding and releasing lithium ions is mainly used, and natural graphite, artificial graphite, amorphous carbon, etc. are listed as representative examples. It is done. Furthermore, metal or alloy negative electrodes using silicon, tin or the like for increasing the capacity are also known. As the positive electrode active material, a transition metal composite oxide capable of mainly inserting and extracting lithium ions is used, and representative examples of the transition metal include cobalt, nickel, manganese, iron and the like.

Since such lithium ion secondary batteries use positive and negative electrodes with high activity, the charge / discharge capacity decreases due to repeated charge / discharge and storage of the battery due to side reactions between the electrodes and the electrolyte. In order to improve battery characteristics, various studies have been made on non-aqueous solvents and electrolytes.
Patent Document 1 proposes that in a lithium secondary battery, the cycle life is extended by using an organic fluorinated ether compound as an electrolyte.

In Patent Document 2, by using a nonaqueous electrolytic solution characterized in that the content of the halogen-substituted ether compound is more than 30% by volume and not more than 90% by volume, the cycle characteristics and the low-temperature discharge characteristics are excellent, and the safety. It has been proposed to be excellent.
Patent Document 3 proposes that cycle characteristics and storage characteristics are excellent by using an electrolytic solution containing a halogen-substituted ether having a specific structure.

Patent Document 4 discloses that a battery having improved storage characteristics can be obtained by containing at least one additive selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate in a non-aqueous electrolyte. Has been proposed.
Patent Document 5 proposes that an output solution and cycle characteristics are excellent by using an electrolyte containing a fluorine atom ether and a monofluorophosphate and / or difluorophosphate.

JP-A-7-249432 JP-A-9-97627 JP-A-11-26015 Japanese Patent Laid-Open No. 11-67270 JP 2008-269982 A

However, the demand for higher performance of batteries in recent years is increasing, and it is required to achieve various battery characteristics such as high capacity, high temperature storage characteristics, and cycle characteristics at a high level.
To increase the capacity, for example, pressurize the active material layer of the electrode to increase the density to reduce the volume occupied by the active material other than the active material inside the battery as much as possible. How to do is being studied. However, when the active material layer of the electrode is pressurized and densified, it becomes difficult to use the active material uniformly, and some lithium precipitates due to a non-uniform reaction or deterioration of the active material is promoted. As a result, a problem that sufficient characteristics cannot be obtained easily occurs. Further, when the use range of the positive electrode is expanded to be used up to a high potential, the activity of the positive electrode is further increased, and the problem that the deterioration is accelerated by the reaction between the positive electrode and the electrolytic solution is likely to occur. In particular, when stored under high temperature conditions in a charged state, it is known that the battery capacity decreases due to a side reaction between the electrode and the electrolyte solution. In order to improve storage characteristics, various non-aqueous solvents and electrolytes are used. Consideration has been made.

Further, the increase in capacity reduces the gap in the battery, and there is a problem that the internal pressure of the battery increases remarkably even when a small amount of gas is generated by the decomposition of the electrolyte.
Therefore, for high-temperature storage characteristics, it is required to suppress gas generation, but the non-aqueous electrolyte secondary battery using the electrolyte described in Patent Documents 1 to 5 was not satisfactory. .

Moreover, although the initial efficiency was improved by using a fluorine-substituted ether, sufficient low-temperature discharge characteristics could not be obtained because the viscosity of the electrolytic solution increased and the electrical conductivity decreased.
The present invention has been made to solve the above-described conventional problems, and is used for a non-aqueous electrolyte secondary battery that is excellent in initial efficiency and low-temperature discharge characteristics and has a reduced amount of gas generated during high-temperature storage. It is an object to provide a non-aqueous electrolyte solution and a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte solution.

As a result of various studies to achieve the above object, the present inventors have found that the above problems can be solved by including a specific compound in the electrolytic solution, and have completed the present invention. .
That is, the gist of the present invention is as follows.
(1) A non-aqueous electrolyte solution for use in a non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of occluding and releasing lithium ions, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution has the chemical formula (I And a monofluorophosphate and / or a difluorophosphate.

(In the formula, Rf ₁ represents a hydrogen atom, a fluorine atom, an alkyl group in which at least some of the hydrogen atoms are substituted with fluorine atoms, or an alkoxyalkyl group in which at least some of the hydrogen atoms are substituted with fluorine atoms. Rf ₂ represents an alkyl group in which at least some of the hydrogen atoms are substituted with fluorine atoms, excluding one hydrogen atom bonded to the terminal carbon atom, or alkoxy in which at least some of the hydrogen atoms are optionally substituted with fluorine atoms Represents an alkyl group.)
(2) In the chemical formula (I), Rf ₁ represents a hydrogen atom, a fluorine atom, a methyl group in which at least a part of the hydrogen atoms are substituted with a fluorine atom, and Rf ₂ is bonded to a terminal carbon atom. An alkyl group having 1 to 3 carbon atoms in which at least some hydrogen atoms are substituted with fluorine atoms, excluding hydrogen atoms, or an alkoxyalkyl having 2 to 5 carbon atoms in which at least some hydrogen atoms may be substituted with fluorine atoms The non-aqueous electrolyte solution according to (1) above, which represents a group.
(3) A non-aqueous electrolyte used in a non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of occluding and releasing lithium ions, and a non-aqueous electrolyte, and represented by the chemical formula (I) It contains three or more kinds of cyclic carbonate compounds including a substituted ether and ethylene carbonate and a cyclic carbonate compound having a carbon-carbon unsaturated bond, and the volume of ethylene carbonate is smaller than the total amount of other cyclic carbonate compounds. Non-aqueous electrolyte.
(4) In the chemical formula (I), Rf ₁ represents a hydrogen atom, a fluorine atom, a methyl group in which at least a part of the hydrogen atoms are substituted with a fluorine atom, and Rf ₂ is one bonded to the terminal carbon atom. An alkyl group having 1 to 3 carbon atoms in which at least some hydrogen atoms are substituted with fluorine atoms, excluding hydrogen atoms, or an alkoxyalkyl having 2 to 5 carbon atoms in which at least some hydrogen atoms may be substituted with fluorine atoms The non-aqueous electrolyte solution according to (3) above, which represents a group.
(5) The cyclic carbonate compound represented by the chemical formula (II) is contained as a cyclic carbonate compound other than ethylene carbonate and a cyclic carbonate compound having a carbon-carbon unsaturated bond. The non-aqueous electrolyte solution described in 1.

(In the formula, R ₁ to R ₄ represent a hydrogen atom, a halogen atom, or a methyl group or an ethyl group in which the hydrogen atom may be substituted with a halogen atom.)
(6) The nonaqueous electrolytic solution according to any one of (3) to (5) above, further comprising a monofluorophosphate and / or a difluorophosphate.
(7) A non-aqueous electrolyte secondary battery including a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is any one of the above (1) to (6) A non-aqueous electrolyte secondary battery, wherein the non-aqueous electrolyte solution is described.

  According to the present invention, it is possible to provide a non-aqueous electrolyte battery that is excellent in initial efficiency and low-temperature discharge characteristics and in which the amount of gas generated after high-temperature storage is suppressed.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented without departing from the gist of the present invention.
<Non-aqueous electrolyte>
The non-aqueous electrolyte solution according to claim 1 of the present invention, like a general non-aqueous electrolyte solution, usually has an electrolyte and a non-aqueous solvent for dissolving it as a main component, and further has a chemical formula (I) And a monofluorophosphate and / or a difluorophosphate are contained in the non-aqueous electrolyte solution.

  The non-aqueous electrolyte solution according to claim 3 of the present invention, like a general non-aqueous electrolyte solution, usually has an electrolyte and a non-aqueous solvent for dissolving it as a main component, and further has a chemical formula (I) A total of three or more cyclic carbonate compounds including ethylene carbonate and a cyclic carbonate compound having a carbon-carbon unsaturated bond, and the volume of ethylene carbonate is the total amount of the other cyclic carbonate compounds. Fewer.

  The fluorine-substituted ether contained in the nonaqueous electrolytic solution of the present invention is not particularly limited as long as it has a structure represented by the chemical formula (I), but the molecular weight of the compound is usually 114 or more, usually 1000 or less, preferably 500 or less. The fluorine-substituted ether represented by the chemical formula (I) may be used alone or in combination of two or more. Since the fluorine-substituted ether having the structure of the chemical formula (I) has a preferable dielectric constant and vapor pressure, it is excellent in compatibility with other solvents and generates a small amount of gas during high-temperature storage.

The fluorine-substituted ether contained in the non-aqueous electrolyte solution of the present invention, in chemical formula (I), Rf ₁ represents a hydrogen atom, a fluorine atom, a methyl group in which at least some of the hydrogen atoms are substituted with fluorine atoms, Rf ₂ is an alkyl group having 1 to 3 carbon atoms in which at least a part of the hydrogen atoms are substituted with fluorine atoms, excluding one hydrogen atom bonded to the terminal carbon atom, or at least a part of the hydrogen atoms are substituted with fluorine It is preferable that it is a compound which shows the C2-C5 alkoxyalkyl group which may be made.

  The content of the fluorine-substituted ether represented by the chemical formula (I) in the non-aqueous electrolyte is preferably 0.001% by mass or more, and more preferably 0.01% by mass or more. If the concentration is too low, the effects of the present invention may hardly be exhibited. On the other hand, if the concentration is too high, the electric conductivity tends to be low and the charge / discharge capacity of the battery tends to be reduced. It is.

Specific examples of the fluorine-substituted ether represented by the chemical formula (I) include the following compounds.
CF ₃ CH ₂ OCF ₂ H
CF ₃ CH ₂ OCHF ₂
CF ₂ HCH ₂ OCF ₂ H
CF ₂ HCH ₂ OCHF ₂
CF ₃ CH ₂ OCF ₂ CF ₂ H
CF ₃ CH ₂ OCH ₂ CF ₂ H
CF ₃ CH ₂ OCF ₂ CH ₃
CF ₂ HCH ₂ OCF ₂ CF ₂ H
CF ₂ HCH ₂ OCH ₂ CF ₂ H
CF ₂ HCH ₂ OCH ₂ CFH ₂
CF ₂ HCH ₂ OCF ₂ CH ₃
CF ₃ CF ₂ CH ₂ OCF ₂ CF ₂ H
CF ₂ HCF ₂ CH ₂ OCF ₂ CF ₂ H
CFH ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H
CF ₃ CF ₂ CH ₂ OCF ₂ CF ₂ CF ₂ H
CF ₂ HCF ₂ CH ₂ OCF ₂ CF ₂ CF ₂ H
CF ₂ HCF ₂ CH ₂ OCH ₂ CF ₂ CF ₂ H
CF ₂ HCF ₂ CH ₂ OCH ₂ CH ₂ CF ₂ H
CF ₃ CH ₂ OCH ₂ OCF ₃
CF ₂ HCH ₂ OCH ₂ OCF ₃
CF ₃ CH ₂ OCH ₂ OCH ₃
CF ₂ HCH ₂ OCH ₂ CH ₂ OCH ₃
CF ₂ HCH ₂ OCH ₂ CH ₂ OCF ₃
CF ₂ HCH ₂ OCH ₂ CH ₂ OCF ₂ CF ₂ H
CF ₃ CH ₂ OCF ₂ CF ₂ OCF ₂ CF ₃
CF ₃ CH ₂ OCF ₂ CF ₂ OCF ₂ CF ₂ H
CF ₃ CH ₂ OCH ₂ CH ₂ OCH ₂ CF ₃
CF ₃ CH ₂ OCH ₂ CH ₂ OCH ₂ CH ₃
CF ₃ CH ₂ OCH ₂ CH ₂ OCH ₂ CH ₂ CF ₃
CF ₃ CH ₂ OCH ₂ CH ₂ OCH ₂ CH ₂ CH ₃
CF ₂ HCH ₂ OCH ₂ CH ₂ OCF ₂ CF ₂ H
CF ₂ HCH ₂ OCF ₂ CH ₂ OCF ₂ CF ₂ H
CF ₃ CF ₂ OCF ₂ CH ₂ OCF ₂ CF ₂ H
CF ₃ CH ₂ OCF (CF ₃ ) CF ₂ H
CF ₃ CH ₂ OCF (CF ₂ H) CF ₂ H
CF ₃ CH ₂ OCF (C ₂ F ₅ ) CF ₂ H
Above all,
CF ₃ CH ₂ OCF ₂ H
CF ₂ HCH ₂ OCF ₂ H
CF ₃ CH ₂ OCF ₂ CF ₂ H
CF ₃ CH ₂ OCF ₂ CH ₃
CF ₂ HCH ₂ OCF ₂ CF ₂ H
CF ₂ HCH ₂ OCH ₂ CF ₂ H
CF ₂ HCH ₂ OCF ₂ CH ₃
CF ₃ CF ₂ CH ₂ OCF ₂ CF ₂ H
CF ₂ HCF ₂ CH ₂ OCF ₂ CF ₂ H
CFH ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H
CF ₃ CF ₂ CH ₂ OCF ₂ CF ₂ CF ₂ H
CF ₂ HCF ₂ CH ₂ OCF ₂ CF ₂ CF ₂ H
CF ₂ HCH ₂ OCH ₂ OCF ₃
CF ₂ HCH ₂ OCH ₂ CH ₂ OCF ₂ CF ₂ H
CF ₃ CH ₂ OCF ₂ CF ₂ OCF ₂ CF ₃
CF ₃ CH ₂ OCF ₂ CF ₂ OCF ₂ CF ₂ H
CF ₃ CH ₂ OCH ₂ CH ₂ OCH ₂ CF ₃
CF ₃ CH ₂ OCH ₂ CH ₂ OCH ₂ CH ₃
CF ₃ CH ₂ OCH ₂ CH ₂ OCH ₂ CH ₂ CF ₃
CF ₂ HCH ₂ OCH ₂ CH ₂ OCF ₂ CF ₂ H
CF ₃ CF ₂ OCF ₂ CH ₂ OCF ₂ CF ₂ H
CF ₃ CH ₂ OCF (C ₂ F ₅ ) CF ₂ H
Is preferred, and
CF ₂ HCH ₂ OCF ₂ H
CF ₃ CH ₂ OCF ₂ CF ₂ H
CF ₂ HCH ₂ OCF ₂ CF ₂ H
CF ₂ HCH ₂ OCH ₂ CF ₂ H
CF ₃ CF ₂ CH ₂ OCF ₂ CF ₂ H
CF ₂ HCF ₂ CH ₂ OCF ₂ CF ₂ H
CF ₂ HCH ₂ OCH ₂ OCF ₃
CF ₂ HCH ₂ OCH ₂ CH ₂ OCF ₂ CF ₂ H
CF ₃ CH ₂ OCH ₂ CH ₂ OCH ₂ CF ₃
CF ₃ CH ₂ OCH ₂ CH ₂ OCH ₂ CH ₃
CF ₃ CH ₂ OCH ₂ CH ₂ OCH ₂ CH ₂ CF ₃
CF ₃ CF ₂ OCF ₂ CH ₂ OCF ₂ CF ₂ H
CF ₃ CH ₂ OCF (C ₂ F ₅ ) CF ₂ H
Is preferred.

Among the above compounds, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (CF ₂ HCF ₂ CH ₂ OCF ₂ CF ₂ H), 1,1,2,2 - tetrafluoroethyl 2,2,3,3,3-pentafluoro-propyl ether _{(CF 3 CF 2 CH 2 OCF} 2 CF 2 H), ethoxy-2,2,2-trifluoro-ethoxy - ethane _(CF 3 CH ₂ OCH ₂ CH ₂ OCH ₂ CH ₃ ) is particularly preferred.

[Monofluorophosphate and difluorophosphate]
The nonaqueous electrolytic solution according to claim 1 of the present invention contains a monofluorophosphate and / or a difluorophosphate.
The counter cations of monofluorophosphate and difluorophosphate are not particularly limited, but lithium, sodium, potassium, magnesium, calcium, and NR ¹ R ² R ³ R ⁴ (wherein R ^{1 to} R ⁴ Are each independently a hydrogen atom or an organic group having 1 to 12 carbon atoms.)

Although it does not specifically limit as a C1-C12 organic group represented by R < ¹ > -R < ⁴ > of the said ammonium, For example, it is substituted by the alkyl group, the halogen atom, or the alkyl group which may be substituted by the halogen atom. Examples thereof include an cycloalkyl group which may be substituted, an aryl group which may be substituted with a halogen atom or an alkyl group, and a nitrogen atom-containing heterocyclic group which may have a substituent. Among these, as R ^{1 to} R ⁴ , a hydrogen atom, an alkyl group, a cycloalkyl group, or a nitrogen atom-containing heterocyclic group is preferable.

  Specific examples of monofluorophosphate and difluorophosphate include lithium monofluorophosphate, sodium monofluorophosphate, potassium monofluorophosphate, lithium difluorophosphate, sodium difluorophosphate, and potassium difluorophosphate. And lithium monofluorophosphate and lithium difluorophosphate are preferable, and lithium difluorophosphate is more preferable.

These may be used alone or in combination of two or more.
Generally, the use of a fluorine-substituted ether represented by the chemical formula (I) increases the resistance during discharge, but the combined use with monofluorophosphate and / or difluorophosphate increases the resistance during discharge. Since it can suppress, it is preferable.
The proportion of monofluorophosphate and / or difluorophosphate in the non-aqueous electrolyte solution according to claim 1 of the present invention is preferably 0.001 wt% or more, more preferably 0.01 wt% or more, and further Preferably it is 0.1 weight% or more, Especially preferably, it is 0.2 weight% or more, Preferably it is 5 weight% or less, More preferably, it is 3 weight% or less, More preferably, it is 2 weight% or less. If the concentration is lower than this, the effects of the present invention may be hardly exhibited. On the other hand, if the concentration is too high, precipitation tends to occur at low temperatures.

The non-aqueous electrolyte solution of the invention according to claim 3 contains three or more kinds of cyclic carbonates including ethylene carbonate and a cyclic carbonate having a carbon-carbon unsaturated bond.
The volume of ethylene carbonate in the non-aqueous electrolyte is less than the total volume of other cyclic carbonate compounds. By making the volume of ethylene carbonate smaller than the total volume of the other cyclic carbonate compounds, it is possible to suppress gas generation due to the side reaction of ethylene carbonate on the electrode.

  The ratio of the volume of ethylene carbonate to the total volume of other cyclic carbonate compounds in the non-aqueous electrolyte is preferably 0.01 or more, more preferably 0.1 or more, and particularly preferably 0.2. Above, preferably less than 1, more preferably 0.9 or less, and particularly preferably 0.8 or less. If the amount is too small, battery characteristics such as cycle characteristics may be deteriorated. If the amount is too large, the amount of generated gas increases.

[Cyclic carbonate compound having a carbon-carbon unsaturated bond]
Examples of the cyclic carbonate compound having a carbon-carbon unsaturated bond include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, 1,2-diethyl vinylene carbonate, fluoro vinylene carbonate, trifluoromethyl. Vinylene carbonate compounds such as vinylene carbonate; vinyl ethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, 1-n-propyl-2-vinylethylene carbonate, 1-methyl-2- Vinyl ethylene carbonate compounds such as vinyl ethylene carbonate, 1,1-divinyl ethylene carbonate, 1,2-divinyl ethylene carbonate; 1,1-dimethyl-2- Methylene ethylene carbonate compounds such as tylene ethylene carbonate and 1,1-diethyl-2-methylene ethylene carbonate; ethynyl ethylene carbonate compounds such as ethynyl ethylene carbonate and 1,2-diethynyl ethylene carbonate, 1,2-diphenyl carbonate, 1, Examples thereof include ethylene carbonate compounds having an aryl group such as 2-di (phenylcyclohexyl) ethylene carbonate and 1,2-di (biphenyl) ethylene carbonate. Among these, vinylene carbonate, vinyl ethylene carbonate, and 1,2-divinyl ethylene carbonate are preferable from the viewpoint of improving cycle characteristics and capacity maintenance characteristics after high-temperature storage, among which vinylene carbonate or vinyl ethylene carbonate is more preferable, and vinylene carbonate is particularly preferable. preferable. These may be used alone or in combination of two or more.

When using 2 or more types together, it is preferable to use together vinylene carbonate and vinyl ethylene carbonate.
The proportion of the cyclic carbonate compound having a carbon-carbon unsaturated bond in the non-aqueous electrolyte is usually 0.01% by weight or more, preferably 0.1% by weight or more, particularly preferably 0.3% by weight or more, most preferably. Is 0.5% by weight or more. When there are too few cyclic carbonate compounds which have a carbon-carbon unsaturated bond, the effect of improving the cycling characteristics of a battery and the capacity maintenance characteristics after high temperature storage may not be fully exhibited. However, if the content of the cyclic carbonate compound having a carbon-carbon unsaturated bond is too large, the amount of gas generated may increase during high-temperature storage, so that it is usually 8% by weight or less, preferably 4% by weight or less, The amount is particularly preferably 3% by weight or less.

  Of the three types of cyclic carbonate compounds contained in the non-aqueous electrolyte solution according to claim 3, the cyclic carbonate compound other than ethylene carbonate and a cyclic carbonate having a carbon-carbon unsaturated bond is a cyclic represented by the chemical formula (II). It is preferably a carbonate compound, more preferably an asymmetric cyclic carbonate compound or a carbonate compound having a fluorine atom.

(In the formula, R ₁ to R ₄ represent a hydrogen atom, a halogen atom, or a methyl group or an ethyl group in which the hydrogen atom may be substituted with a halogen atom.)

[Cyclic carbonate compounds other than ethylene carbonate and cyclic carbonate having a carbon-carbon unsaturated bond]
(Asymmetric cyclic carbonate compound)
Examples of the asymmetric cyclic carbonate compound include propylene carbonate, butylene carbonate, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-5-methyl-1,3-dioxolan-2-one, 4,4,5-trimethyl-1,3-dioxolan-2-one, 4-propityl-1,3-dioxolan-2-one, 4-methyl-1,3-dioxan-2-one, 4,5- Dimethyl-1,3-dioxan-2-one, 4,4,6-trimethyl-1,3-dioxan-2-one, 5-methyl-5-ethyl-1,3-dioxan-2-one, etc. Can be mentioned.

(Cyclic carbonate compound having a fluorine atom)
Examples of the cyclic carbonate compound having a fluorine atom include fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, tetrafluoroethylene carbonate, 1- Fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, 1,1-difluoro -2,2-dimethylethylene carbonate, trifluoromethylethylene carbonate, and the like.

  Of these, butylene carbonate, propylene carbonate, and fluoroethylene carbonate are particularly preferable as the cyclic carbonate compound other than ethylene carbonate and cyclic carbonate having a carbon-carbon unsaturated bond. These may be used alone or in combination of two or more. The cyclic carbonate compound other than ethylene carbonate and cyclic carbonate having a carbon-carbon unsaturated bond is usually 5% by volume or more, preferably 10% by volume or more, more preferably 15% by volume or more, and usually 90% by volume or less, preferably Is preferably 80% by volume or less, more preferably 70% by volume or less. When the amount is less than the above range, the degree of dissociation of the electrolyte is reduced, so that the charge / discharge efficiency is lowered. When the amount is more than the above range, the viscosity of the electrolytic solution is increased, so that the low temperature discharge characteristics may be lowered.

  The non-aqueous electrolyte solution according to claim 3 of the present invention can contain a morphofluorophosphate and / or a difluorophosphate. The proportion of monofluorophosphate and / or difluorophosphate in the non-aqueous electrolyte solution according to claim 5 of the present invention is preferably 0.001 wt% or more, more preferably 0.01 wt% or more, and further Preferably it is 0.1 weight% or more, Especially preferably, it is 0.2 weight% or more, Preferably it is 5 weight% or less, More preferably, it is 3 weight% or less, More preferably, it is 2 weight% or less. If the concentration is lower than this, the effects of the present invention may be hardly exhibited. On the other hand, if the concentration is too high, precipitation tends to occur at low temperatures.

[Nonaqueous solvent]
The non-aqueous solvent can be appropriately selected from known solvents for the non-aqueous electrolyte solution without departing from the present invention. Examples thereof include cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, cyclic carboxylic acid esters, chain carboxylic acid esters, sulfur-containing organic solvents, and phosphorus-containing organic solvents.
As cyclic carbonates, ethylene carbonate, propylene carbonate, butylene carbonate, dimethylethylene carbonate, trimethylene carbonate, 4-methyl-1,3-dioxane-2-one, 5-methyl-1,3-dioxane-2-one An alkylene group having 2 to 8 carbon atoms such as 4,6-dimethyl-1,3-dioxan-2-one, 5-methyl-5-propyl-1,3-dioxan-2-one and neopentylene carbonate; Among them, ethylene carbonate, butylene carbonate, and propylene carbonate are preferable from the viewpoint of improving battery characteristics. Further, a part of hydrogen of these compounds may be substituted with fluorine.

As the chain carbonates, dialkyl carbonates are preferable, and the number of carbon atoms of the alkyl group is preferably 1 to 5, and more preferably 1 to 4, respectively. Further, a part of hydrogen of the alkyl group may be substituted with fluorine.
Specifically, for example, symmetric chain alkyl carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; asymmetric chain alkyls such as ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate Examples thereof include dialkyl carbonates such as carbonates. Among these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable from the viewpoint of improving battery characteristics.

Examples of the cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran and the like, and compounds obtained by substituting a part of hydrogen of these compounds with fluorine.
Examples of the chain ethers include dimethoxyethane, diethoxyethane and the like, and compounds in which part of hydrogen of these compounds is substituted with fluorine.
Examples of the cyclic carboxylic acid esters include γ-butyrolactone, γ-valerolactone, and the like, and compounds obtained by substituting a part of hydrogen of these compounds with fluorine.

  Examples of chain carboxylates include methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, propion Examples include isopropyl acid, methyl butyrate, ethyl butyrate, propyl butyrate, methyl valerate, ethyl valerate, etc., and compounds in which part of hydrogen of these compounds such as propyl trifluoroacetate and butyl trifluoroacetate is substituted with fluorine. Methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, and methyl valerate are more preferred.

Examples of the sulfur-containing organic solvent include sulfolane, 2-methylsulfolane, 3-methylsulfolane, diethylsulfone and the like, and compounds obtained by substituting a part of hydrogen of these compounds with fluorine.
Examples of phosphorus-containing organic solvents include trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene methyl phosphate, ethylene ethyl phosphate, etc., and compounds in which part of hydrogen in these compounds is substituted with fluorine Is mentioned.

These may be used alone or in combination of two or more, but it is preferable to use in combination of two or more. For example, it is preferable to use a high dielectric constant solvent such as alkylene carbonates or cyclic carboxylic acid esters in combination with a low viscosity solvent such as dialkyl carbonates or chain carboxylic acid esters.
In the non-aqueous electrolyte solution according to claim 1 of the present invention, one of the preferable combinations of the non-aqueous solvents is a combination mainly composed of ethylene carbonate and dialkyl carbonate. Among them, the total of ethylene carbonate and dialkyl carbonate in the nonaqueous solvent is 70% by volume or more, preferably 80% by volume or more, more preferably 90% by volume or more, and relative to the total of ethylene carbonate and dialkyl carbonate. The proportion of ethylene carbonate is 5% by volume or more, preferably 10% by volume or more, more preferably 15% by volume or more, usually 50% by volume or less, preferably 35% by volume or less, more preferably 30% by volume or less, and still more preferably Is 25% by volume or less. Use of a combination of these non-aqueous solvents is preferable because the balance between the cycle characteristics and high-temperature storage characteristics (particularly, the remaining capacity and high-load discharge capacity after high-temperature storage) of a battery produced using the non-aqueous solvent is improved.

  Specific examples of preferred combinations of ethylene carbonate and dialkyl carbonate include ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate and ethyl methyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate and ethyl methyl. Examples thereof include carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

A combination in which propylene carbonate is further added to a combination of these ethylene carbonate and dialkyl carbonates is also mentioned as a preferable combination.
In the case of containing propylene carbonate, the volume ratio of ethylene carbonate to propylene carbonate (ethylene carbonate / propylene carbonate) is preferably 0.4 or more, more preferably 1.0 or more, and particularly preferably 1.5 or more. . Furthermore, the lower limit of the proportion of propylene carbonate in the entire non-aqueous solvent is usually 0.1% by volume or more, preferably 1% by volume or more, more preferably 2% by volume or more, and the upper limit is usually 20% by volume or less. Preferably it is 8 volume% or less, More preferably, it is 5 volume% or less. It is preferable to contain propylene carbonate in this concentration range because the low temperature characteristics are further excellent while maintaining the characteristics of the combination of ethylene carbonate and dialkyl carbonate.

  Among the combinations of ethylene carbonate and dialkyl carbonate, those containing asymmetrical chain alkyl carbonates as dialkyl carbonate are more preferred, especially ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate. Those containing ethylene carbonate, symmetric chain alkyl carbonates, and asymmetric chain alkyl carbonates such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferred because of a good balance between cycle characteristics and large current discharge characteristics. Among them, the asymmetric chain alkyl carbonate is preferably ethyl methyl carbonate, and the alkyl group of the alkyl carbonate preferably has 1 to 2 carbon atoms.

  When diethyl carbonate is contained in the non-aqueous solvent, the lower limit of the proportion of diethyl carbonate in the total non-aqueous solvent is usually 10% by volume or more, preferably 20% by volume or more, more preferably 25% by volume. More preferably, it is 30% by volume or more, and the upper limit is usually 90% by volume or less, preferably 80% by volume or less, more preferably 75% by volume or less, and further preferably 70% by volume or less. When contained, gas generation during high-temperature storage is suppressed, which is preferable.

  In the case where dimethyl carbonate is contained in the non-aqueous solvent, the lower limit of the proportion of dimethyl carbonate in the total non-aqueous solvent is usually 10% by volume or more, preferably 20% by volume or more, more preferably 25% by volume. Or more, more preferably 30% by volume or more, and the upper limit is usually 90% by volume or less, preferably 80% by volume or less, more preferably 75% by volume or less, and further preferably 70% by volume or less. This is preferable because the load characteristics of the battery are improved.

Above all, it contains dimethyl carbonate and ethyl methyl carbonate, and by increasing the content ratio of dimethyl carbonate over the content ratio of ethyl methyl carbonate, the battery characteristics after high-temperature storage are improved while ensuring the electrical conductivity of the electrolyte. This is preferable.
The lower limit of the capacity ratio of dimethyl carbonate to ethyl methyl carbonate (dimethyl carbonate / ethyl methyl carbonate) in all non-aqueous solvents improves the electrical conductivity of the electrolyte and the battery characteristics after storage. 1 or more is preferable, 1.5 or more is more preferable, and 2.5 or more is more preferable. The upper limit of the capacity ratio (dimethyl carbonate / ethyl methyl carbonate) is preferably 40 or less, more preferably 20 or less, still more preferably 10 or less, and particularly preferably 8 or less, in order to improve battery characteristics at low temperatures.

In addition, in the combination mainly composed of the alkylene carbonates and dialkyl carbonates, other solvents may be mixed.
Another example of a preferable non-aqueous solvent is that one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, and butylene carbonate, or a mixed solvent consisting of two or more organic solvents selected from the group is the whole. It occupies 40% by volume or more. The non-aqueous electrolyte using this mixed solvent is less likely to evaporate or leak when used at high temperatures. Among them, the total of ethylene carbonate and propylene carbonate in the nonaqueous solvent is 50% by volume or more, preferably 60% by volume or more, more preferably 70% by volume or more, and the volume ratio of ethylene carbonate to propylene carbonate (ethylene When a carbonate / propylene carbonate) of 1.0 or less, preferably 0.9 or less is used, the balance between cycle characteristics and high-temperature storage characteristics is generally improved.

Moreover, the non-aqueous electrolyte solution according to claim 1 of the present invention may be used in combination with a cyclic carbonate compound having a carbon-carbon unsaturated bond or a cyclic carbonate compound having a fluorine atom, thereby improving cycle characteristics and high temperature storage characteristics. From this point, it is preferable to use in combination.
In the non-aqueous electrolyte solution according to claim 3 of the present invention, preferable examples of the non-aqueous solvent include, in addition to ethylene carbonate and a cyclic carbonate compound having a carbon-carbon unsaturated bond, fluoroethylene carbonate, butylene carbonate, propylene carbonate, and A combination of one or more organic solvents selected from the group consisting of fluoroethylene carbonate and dialkyl carbonates. Among these, when the dialkyl carbonates in the non-aqueous solvent are 20% by volume or more, preferably 30% by volume or more, more preferably 40% by volume or more, the balance between high temperature storage characteristics and low temperature discharge characteristics is improved. .
In the present specification, the capacity of the non-aqueous solvent is a measured value at 25 ° C., but a measured value at the melting point is used for a solid at 25 ° C. such as ethylene carbonate.

[Electrolytes]
There is no restriction | limiting in the electrolyte used for the non-aqueous electrolyte solution of this invention, A well-known thing can be used arbitrarily if it is used as an electrolyte for the target non-aqueous electrolyte secondary battery.
When the nonaqueous electrolytic solution of the present invention is used for a lithium secondary battery, a lithium salt is usually used as an electrolyte.
Specific examples of the electrolyte include inorganic lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , and LiBF ₄ ; LiFSO ₃ , LiCF ₃ SO ₃ , LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN ( C ₂ F ₅ SO ₂ ) ₂ , lithium cyclic 1,2-tetrafluoroethanedisulfonylimide, lithium cyclic 1,3-hexafluoropropane disulfonylimide, LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) , LiC (CF ₃ SO ₂ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₄ (C ₂ F ₅ ) ₂ , LiPF ₄ (CF ₃ SO ₂ ) ₂ , LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ , Fluorine-containing organic lithium salts such as LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , LiBF ₂ (CF ₃ SO ₂ ) ₂ , LiBF ₂ (C ₂ F ₅ SO ₂ ) ₂ ; lithium bis ( Oxalato) And dicarboxylic acid-containing lithium salts such as borate, lithium tris (oxalato) phosphate, lithium difluorooxalatoborate, lithium difluorobis (oxalato) phosphate; and the like.

Among these, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , lithium cyclic 1,2-tetrafluoroethanedisulfonylimide, lithium cyclic 1,3-hexafluoropropane disulfonylimide is preferable, and LiPF ₆ and LiBF ₄ are particularly preferable.
Moreover, these lithium salts may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio. Among these, the combination of two kinds of specific inorganic lithium salts and the combined use of inorganic lithium salts and fluorine-containing organic lithium salts are preferable because gas generation during high-temperature storage is suppressed or deterioration after high-temperature storage is suppressed. .

In particular, the combination and the LiPF ₆ and LiBF _4, and an inorganic lithium salt such as _{LiPF 6, LiBF 4, LiCF 3} SO 3, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, lithium It is preferable to use in combination with a fluorine-containing organic lithium salt such as cyclic 1,2-tetrafluoroethanedisulfonylimide and lithium cyclic 1,3-hexafluoropropane disulfonylimide.

When used in combination LiPF ₆ and LiBF ₄ are the content of LiBF ₄ to the total of LiPF ₆ and LiBF ₄ is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, particularly preferably It is 0.1% by mass or more, preferably 20% by mass or less, more preferably 10% by mass or less, particularly preferably 5% by mass or less, and most preferably 3% by mass or less. If it is less than this range, the desired effect may not be obtained, and if it exceeds this range, battery characteristics such as high load discharge characteristics may deteriorate.

On the other hand, inorganic lithium salts such as LiPF ₆ and LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , lithium cyclic 1,2-tetrafluoroethanedisulfonyl When the imide and the fluorine-containing organic lithium salt such as lithium cyclic 1,3-hexafluoropropanedisulfonylimide are used in combination, the content of the inorganic lithium salt in the total of both is 70% by mass or more and 99% by mass or less. It is desirable that

  The concentration of these electrolytes in the non-aqueous electrolyte solution is not particularly limited in order to exhibit the effects of the present invention, but is usually 0.5 mol / liter or more, preferably 0.8 mol / liter or more, more The amount is preferably 1.0 mol / liter or more, more preferably 1.1 mol / liter or more, and particularly preferably 1.2 mol / liter or more. Further, it is usually 3 mol / liter or less, preferably 2 mol / liter or less, more preferably 1.8 mol / liter or less, and still more preferably 1.6 mol / liter or less. If the concentration is too low, the electrical conductivity of the electrolyte solution may be insufficient. On the other hand, if the concentration is too high, the electrical conductivity may decrease due to an increase in viscosity, and the battery performance may decrease. .

[Other compounds]
The nonaqueous electrolytic solution according to the present invention may contain various other compounds such as a conventionally known overcharge inhibitor as an auxiliary agent as long as the effects of the present invention are not impaired.
As overcharge inhibitors, alkylbiphenyls such as biphenyl, 2-methylbiphenyl, 2-ethylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclopentylbenzene, cyclohexylbenzene, cis-1-propyl-4-phenylcyclohexane , Trans-1-propyl-4-phenylcyclohexane, cis-1-butyl-4-phenylcyclohexane, trans-1-butyl-4-phenylcyclohexane, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, methylphenyl Carbonate, ethylphenyl carbonate, diphenyl carbonate, triphenyl phosphate, tris (2-tert-butylphenyl) phosphate, tris (3-tert-butylphenyl) phosphate, tris (4- -Butylphenyl) phosphate, tris (2-t-amylphenyl) phosphate, tris (3-t-amylphenyl) phosphate, tris (4-t-amylphenyl) phosphate, tris (2-cyclohexylphenyl) phosphate, tris ( Aromatic compounds such as 3-cyclohexylphenyl) phosphate and tris (4-cyclohexylphenyl) phosphate; 2-fluorobiphenyl, 3-fluorobiphenyl, 4-fluorobiphenyl, 4,4′-difluorobiphenyl, o-cyclohexylfluorobenzene, Partially fluorinated products of the above aromatic compounds such as p-cyclohexylfluorobenzene; fluorine-containing anisols such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole And the like.

  Among these, alkylbiphenyl such as biphenyl and 2-methylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclopentylbenzene, cyclohexylbenzene, cis-1-propyl-4-phenylcyclohexane, trans-1-propyl-4- Phenylcyclohexane, cis-1-butyl-4-phenylcyclohexane, trans-1-butyl-4-phenylcyclohexane, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, methylphenyl carbonate, diphenyl carbonate, triphenyl phosphate, Aromatic compounds such as tris (4-t-butylphenyl) phosphate and tris (4-cyclohexylphenyl) phosphate; 2-fluorobiphenyl, 3-fluorobiphenyl, 4 -Partially fluorinated products of the above aromatic compounds such as -fluorobiphenyl, 4,4'-difluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, etc. are preferred. Partially hydrogenated terphenyl, cyclopentylbenzene, cyclohexylbenzene, Cis-1-propyl-4-phenylcyclohexane, trans-1-propyl-4-phenylcyclohexane, cis-1-butyl-4-phenylcyclohexane, trans-1-butyl-4-phenylcyclohexane, t-butylbenzene, t -Amylbenzene, methylphenyl carbonate, diphenyl carbonate, triphenyl phosphate, tris (4-tert-butylphenyl) phosphate, tris (4-cyclohexylphenyl) phosphate, o-cyclohex Le fluorobenzene, p- cyclohexyl fluorobenzene more preferably, partially hydrogenated member and cyclohexylbenzene terphenyl is particularly preferred.

  Two or more of these may be used in combination. When two or more types are used in combination, in particular, a partially hydrogenated terphenyl, a combination of cyclohexylbenzene and t-butylbenzene or t-amylbenzene, or a partially hydrogenated biphenyl, alkylbiphenyl, terphenyl or terphenyl. It is overcharged to use together those selected from oxygen-free aromatic compounds such as cyclohexylbenzene, t-butylbenzene and t-amylbenzene and those selected from oxygen-containing aromatic compounds such as diphenyl ether and dibenzofuran. This is preferable from the viewpoint of the balance between prevention characteristics and high-temperature storage characteristics.

  The content ratio of these overcharge inhibitors in the non-aqueous electrolyte is usually 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and further preferably 0.5%. It is 5 mass% or less, and is 5 mass% or less normally, Preferably it is 3 mass% or less, More preferably, it is 2 mass% or less. If the concentration is too low, the desired effect of the overcharge inhibitor may hardly be exhibited. On the other hand, if the concentration is too high, battery characteristics such as high-temperature storage characteristics tend to deteriorate.

  Other auxiliaries include carbonate compounds such as erythritan carbonate, spiro-bis-dimethylene carbonate, methoxyethyl-methyl carbonate, methoxyethyl-ethyl carbonate, ethoxyethyl-methyl carbonate, ethoxyethyl-ethyl carbonate; succinic anhydride Carboxylic acids such as glutaric anhydride, maleic anhydride, itaconic anhydride, citraconic anhydride, glutaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride and phenylsuccinic anhydride Anhydride: dimethyl succinate, diethyl succinate, diallyl succinate, dimethyl maleate, diethyl maleate, diallyl maleate, dipropyl maleate, dibutyl maleate, bis maleate (trifluoro Dicarboxylic acid diester compounds such as bis (pentafluoroethyl) maleate, bis (2,2,2-trifluoroethyl) maleate; 2,4,8,10-tetraoxaspiro [5.5] undecane Spiro compounds such as 3,9-divinyl-2,4,8,10-tetraoxaspiro [5.5] undecane; ethylene sulfite, propylene sulfite, 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1,4-butene sultone, methyl methanesulfonate, ethyl methanesulfonate, methyl-methoxymethanesulfonate, methyl-2-methoxyethanesulfonate, busulfan, diethylene glycol dimethanesulfonate, 1,2-ethanediol bis ( 2,2,2-trifluoroethane Sulfonate), 1,4-butanediol bis (2,2,2-trifluoroethanesulfonate), sulfolane, 3-sulfolene, 2-sulfolene, dimethylsulfone, diethylsulfone, divinylsulfone, diphenylsulfone, N, N-dimethyl Sulfur-containing compounds such as methanesulfonamide, N, N-diethylmethanesulfonamide; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2- Nitrogen-containing compounds such as imidazolidinone and N-methylsuccinimide; charcoal such as heptane, octane, nonane, decane, cycloheptane, methylcyclohexane, ethylcyclohexane, propylcyclohexane, n-butylcyclohexane, t-butylcyclohexane, dicyclohexyl Hydrogen fluoride compounds; Fluorinated benzenes such as fluorobenzene, difluorobenzene and hexafluorobenzene; Fluorinated toluenes such as 2-fluorotoluene, 2-fluorotoluene, 4-fluorotoluene and benzotrifluoride; Acetonitrile, propionitrile, butyronitrile , Nitrile compounds such as malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile; methyl dimethyl phosphinate, ethyl dimethyl phosphinate, ethyl diethyl phosphinate, trimethylphosphonoformate, triethylphosphonoformate, trimethylphosphonoacetate Phosphorus-containing compounds such as triethylphosphonoacetate, trimethyl-3-phosphonopropionate, and triethyl-3-phosphonopropionate. It is below. Among these, ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1,4-butene sultone, busulfan, 1,4 in terms of improving battery characteristics after high-temperature storage -Sulfur-containing compounds such as butanediol bis (2,2,2-trifluoroethanesulfonate); nitrile compounds such as acetonitrile, propionitrile, butyronitrile, malononitrile, succinonitrile, glutaronitrile, adiponitrile, and pimelonitrile are preferable.

Two or more of these may be used in combination.
The content ratio of these auxiliaries in the non-aqueous electrolyte solution is not particularly limited in order to express the effect of the present invention, but is usually 0.01% by mass or more, preferably 0.1% by mass or more, particularly The content is preferably 0.2% by mass or more, usually 8% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, and particularly preferably 1% by mass or less. By adding these auxiliaries, capacity maintenance characteristics and cycle characteristics after high temperature storage can be improved. If the concentration is lower than this lower limit, the effect of the auxiliary agent may be hardly exhibited. Conversely, if the concentration is too high, battery characteristics such as high load discharge characteristics may be degraded.
Of the auxiliaries, fluorinated benzene and toluene fluoride can also be used as a solvent. The concentration of fluorinated benzene at that time is 8% by mass or more and 50% by mass with respect to the entire non-aqueous electrolyte. % Or less is preferable.

[Preparation of electrolyte]
The non-aqueous electrolyte solution according to claim 1 of the present invention includes an electrolyte, a fluorine-substituted ether represented by the chemical formula (I), monofluorophosphoric acid and / or difluorophosphoric acid, and other substances as necessary. The non-aqueous electrolyte solution according to claim 3 of the present invention can be prepared by dissolving a compound. The non-aqueous solvent contains an electrolyte, a fluorine-substituted ether represented by the chemical formula (I), ethylene carbonate, and carbon- It can be prepared by dissolving three or more kinds of carbonate compounds including a cyclic carbonate compound having a carbon unsaturated bond, and if necessary, other compounds.

In preparing the non-aqueous electrolyte solution, each raw material is preferably dehydrated in advance in order to reduce the water content when the electrolyte solution is used. Usually, it is good to dehydrate to 50 ppm or less, preferably 30 ppm or less, particularly preferably 10 ppm or less. Moreover, you may implement dehydration, a deoxidation process, etc. after electrolyte solution preparation.
The non-aqueous electrolyte solution of the present invention is suitable for use as a non-aqueous electrolyte solution for a secondary battery, that is, a non-aqueous electrolyte secondary battery, for example, a lithium secondary battery, among non-aqueous electrolyte batteries. Hereinafter, a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte of the present invention will be described.

<Non-aqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery of the present invention is a non-aqueous electrolyte battery including a negative electrode and a positive electrode capable of occluding and releasing lithium ions, and a non-aqueous electrolyte, and the non-aqueous electrolyte is a non-aqueous electrolyte of the present invention. It is an aqueous electrolyte solution.

[Battery configuration]
The non-aqueous electrolyte secondary battery according to the present invention can occlude and release lithium ions as in the case of a conventionally known non-aqueous electrolyte secondary battery except that it is produced using the non-aqueous electrolyte of the present invention. A non-aqueous electrolyte battery including a negative electrode and a positive electrode and a non-aqueous electrolyte solution. Usually, the positive electrode and the negative electrode are accommodated in a case through a porous film impregnated with the non-aqueous electrolyte solution of the present invention. can get. Therefore, the shape of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and may be any of a cylindrical shape, a square shape, a laminate shape, a coin shape, a large size, and the like.

[Negative electrode]
The negative electrode active material is not particularly limited as long as it can occlude and release lithium ions. Specific examples thereof include carbonaceous materials, alloy-based materials, lithium-containing metal composite oxide materials, and the like.
These negative electrode active materials may be used alone or in combination of two or more. Of these, carbonaceous materials and alloy materials are preferred.
Graphite preferably has a lattice plane (002 plane) d value (interlayer distance) of 0.335 to 0.338 nm, particularly 0.335 to 0.337 nm, as determined by X-ray diffraction using the Gakushin method. The crystallite size (Lc) determined by X-ray diffraction by the Gakushin method is usually 10 nm or more, preferably 50 nm or more, and particularly preferably 100 nm or more. The ash content is usually 1% by mass or less, preferably 0.5% by mass or less, and particularly preferably 0.1% by mass or less.

  The graphite surface coated with amorphous carbon is preferably graphite having a d-value of 0.335 to 0.338 nm on the lattice plane (002 plane) in X-ray diffraction as a core material. A carbonaceous material having a larger d-value on the lattice plane (002 plane) in X-ray diffraction than the core material is attached, and the d-value on the lattice plane (002 plane) in X-ray diffraction is greater than that of the core material and the core material. The ratio with respect to the carbonaceous material having a large is 99/1 to 80/20 in mass ratio. When this is used, a negative electrode having a high capacity and hardly reacting with the electrolytic solution can be produced.

The particle size of the carbonaceous material is a median diameter measured by a laser diffraction / scattering method and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, most preferably 7 μm or more, and usually 100 μm or less, preferably 50 μm or less More preferably, it is 40 micrometers or less, More preferably, it is 30 micrometers or less.
The specific surface area of the carbonaceous material by the BET method is usually 0.3 m ² / g or more, preferably 0.5 m ² / g or more, more preferably 0.7 m ² / g or more, still more preferably 0.8 m ² / g. or more, usually 25.0 m ² / g or less, preferably 20.0 m ² / g, more preferably 15.0 m ² / g or less, still more preferably 10.0 m ² / g or less.

Further, the carbonaceous material is analyzed by Raman spectrum using argon ion laser light, the peak is the peak intensity of the peak P _A in the range of 1570~1620cm ^-1 I _A, in the range of 1300~1400cm ^-1 P If the peak intensity of the _B was I _B, R value represented by the ratio of I _B and _{I a (= I B / I} a) is what is preferably in the range of 0.01 to 0.7. Further, the half width of the peak in the range of 1570～1620Cm ^-1 is, 26cm ^-1 or less, are preferred in particular 25 cm ^-1 or less.

  The alloy material is not particularly limited as long as it can occlude / release lithium, and single metals and alloys forming lithium alloys, or oxides, carbides, nitrides, silicides, sulfides, and phosphides thereof. Any of these compounds may be used. Preferably, it is a material containing a single metal and an alloy forming a lithium alloy, more preferably a material containing a group 13 and group 14 metal / metalloid element (that is, excluding carbon), and further, aluminum, silicon, and It is preferably a simple metal of tin (which may be hereinafter referred to as “specific metal element”), and an alloy or compound containing these elements.

  Examples of the negative electrode active material having at least one element selected from specific metal elements include a single metal element of any one specific metal element, an alloy composed of two or more specific metal elements, one type, or two or more types An alloy composed of the specific metal element and one or more other metal elements, a compound containing one or more specific metal elements, and oxides, carbides, nitrides of the compounds, Examples include composite compounds such as silicides, sulfides, and phosphides. By using these simple metals, alloys or metal compounds as the negative electrode active material, the capacity of the battery can be increased.

  Moreover, the compound which these complex compounds combined with several elements, such as a metal simple substance, an alloy, or a nonmetallic element, can also be mentioned as an example. More specifically, for example, in silicon and tin, an alloy of these elements and a metal that does not operate as a negative electrode can be used. In addition, for example, in the case of tin, a complex compound containing 5 to 6 kinds of elements in combination with a metal that acts as a negative electrode other than tin and silicon, a metal that does not operate as a negative electrode, and a nonmetallic element can also be used. .

Among these negative electrode active materials, since the capacity per unit mass is large when a battery is formed, any one metal element of a specific metal element, an alloy of two or more specific metal elements, oxidation of a specific metal element A material, carbide, nitride or the like is preferable, and silicon and / or tin metal alone, an alloy, an oxide, carbide, nitride, or the like is particularly preferable because of its large capacity per unit mass.
In addition, although the capacity per unit mass is inferior to that of using a single metal or an alloy, the following compounds containing silicon and / or tin are also preferred because of excellent cycle characteristics.

The element ratio of silicon and / or tin to oxygen is usually 0.5 or more, preferably 0.7 or more, more preferably 0.9 or more, and usually 1.5 or less, preferably 1. Silicon and / or tin oxide of 3 or less, more preferably 1.1 or less.
-Element ratio of silicon and / or tin and nitrogen is usually 0.5 or more, preferably 0.7 or more, more preferably 0.9 or more, and usually 1.5 or less, preferably 1. Silicon and / or tin nitride of 3 or less, more preferably 1.1 or less.
The elemental ratio of silicon and / or tin to carbon is usually 0.5 or more, preferably 0.7 or more, more preferably 0.9 or more, and usually 1.5 or less, preferably 1. Silicon and / or tin carbide of 3 or less, more preferably 1.1 or less.
These alloy materials may be in the form of powder or thin film, and may be crystalline or amorphous.

  The average particle diameter of the alloy-based material is not particularly limited in order to exhibit the effects of the present invention, but is usually 50 μm or less, preferably 20 μm or less, particularly preferably 10 μm or less, usually 0.1 μm or more, preferably 1 μm. As described above, it is particularly preferably 2 μm or more. If the particle size is too large, the expansion of the electrode is increased, and the cycle characteristics may be deteriorated. Moreover, when too small, it will become difficult to collect current, and capacity | capacitance may not fully express.

The lithium-containing metal composite oxide material used as the negative electrode active material is not particularly limited as long as it can occlude and release lithium. However, a lithium-titanium composite oxide (hereinafter referred to as “lithium-titanium composite oxide”) (Abbreviated) is preferred.
In addition, a part of lithium or titanium in the lithium titanium composite oxide is selected from the group consisting of other metal elements such as Na, K, Co, Al, Fe, Mg, Cr, Ga, Cu, Zn, and Nb. Those substituted with at least one element are also preferred.

Furthermore, it is a lithium titanium composite oxide represented by Li _x Ti _y M _z O ₄ , and 0.7 ≦ x ≦ 1.5, 1.5 ≦ y ≦ 2.3, and 0 ≦ z ≦ 1.6. It is preferable that the structure at the time of occlusion / release of lithium ions is stable (M is a group consisting of Na, K, Co, Al, Fe, Mg, Cr, Ga, Cu, Zn, and Nb). Represents at least one element selected).

Especially, the structure in the case where x, y, z of the lithium titanium composite oxide represented by Li _x Ti _y M _z O ₄ satisfies any of the following (a) to (c) is a balance of battery performance. Is particularly preferable because
(A) 1.2 ≦ x ≦ 1.4, 1.5 ≦ y ≦ 1.7, z = 0
(B) 0.9 ≦ x ≦ 1.1, 1.9 ≦ y ≦ 2.1, z = 0
(C) 0.7 ≦ x ≦ 0.9, 2.1 ≦ y ≦ 2.3, z = 0
A particularly preferred representative composition is Li _4/3 Ti _5/3 O ₄ in (a), Li ₁ Ti ₂ O ₄ in (b), and Li _4/5 Ti _11/5 O ₄ in (c). .
As for the structure when Z ≠ 0, for example, Li _4/3 Ti _4/3 Al _1/3 O ₄ is preferable.

[Positive electrode]
The positive electrode active material is not particularly limited as long as it can occlude and release lithium ions. A substance containing lithium and at least one transition metal is preferable, and examples thereof include a lithium transition metal composite oxide and a lithium-containing transition metal phosphate compound.
The transition metal of the lithium transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu or the like, and specific examples include lithium / cobalt composite oxide such as LiCoO ₂ or LiNiO ₂ . Lithium / nickel composite oxides, LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ MnO _{3 and} other lithium / manganese composite oxides, and some of the transition metal atoms that are the main components of these lithium transition metal composite oxides In other words, a part of Co in the lithium-cobalt composite oxide such as LiCoO ₂ is replaced with Al, Ti, V, Cr, Mn, Fe, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si. those substituted with other metals like, a part of Ni Al of lithium-nickel composite oxides such as _{LiNiO 2, Ti, V, Cr} , Mn, Fe, Co, Li, Cu, Zn, g, Ga, Zr, those substituted with other metal such as _{Si, LiMnO 2, LiMn 2 O 4} , Li 2 part Al of Mn MnO ₃ and lithium-manganese composite oxide, Ti, V, Cr , Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si and the like substituted with other metals. Among those _{substituted, LiNi 1-ab Mn a Co} b O 2 (a, b each represents a number from 0 to less than 1, except in the case of a, b are both _{0), LiNi 1-cde Co} c _{al d Mg e O 2 (c} , d, but e is a number from 0 to less than 1, c, d, excluding the case of e are both 0) are preferred, more _{LiNi 1-ab Mn a Co b} O ₂ (0 ≦ a <0.4, 0 ≦ b <0.4), LiNi _1-cde Co _c Al _d Mg _e O ₂ (0 ≦ c <0.3, 0 ≦ d <0.1, 0 ≦ e <0.05), particularly LiNi _1/3 Co _01/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.3 Mn _0.2 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _0.85 Co _0.10 Al _0.03 Mg _0.02 O ₂ is preferred.

As the transition metal of the lithium-containing transition metal phosphate compound, V, Ti, Cr, Mn, Fe, Co, Ni, Cu and the like are preferable, and specific examples include, for example, LiFePO ₄ , Li ₃ Fe ₂ (PO ₄ ). ₃ , iron phosphates such as LiFeP ₂ O ₇ , cobalt phosphates such as LiCoPO _4, etc., in which some of the transition metal atoms that are the main components of these lithium transition metal phosphate compounds are substituted with other metals, , LiFePO ₄ , Li ₃ Fe ₂ (PO ₄ ) ₃ , LiFeP ₂ O _{7 and} other iron phosphates such as Fe, Al, Ti, V, Cr, Mn, Co, Li, Ni, Cu, Zn Al, Ti, V, Cr, Mn, Fe, Li, Ni, a part of Co of cobalt phosphates such as LiCoPO ₄ substituted with other metals such as Mg, Ga, Zr, Nb, and Si Cu, Zn, Mg, Ga, Z Examples include those substituted with other metals such as r, Nb, and Si.

These positive electrode active materials may be used alone or in combination.
In addition, a material in which a substance (surface adhering substance) having a composition different from that of the substance constituting the main cathode active material is attached to the surface of the cathode active material can be used. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate And sulfates such as aluminum sulfate and carbonates such as lithium carbonate, calcium carbonate and magnesium carbonate.

  The amount of the surface adhering substance is not particularly limited in order to exhibit the effect of the present invention, but is preferably 0.1 ppm or more, more preferably 1 ppm or more, and still more preferably, by mass with respect to the positive electrode active material. It is used at 10 ppm or more, preferably 20% or less, more preferably 10% or less, and still more preferably 5% or less. The surface adhering substance can suppress the oxidation reaction of the non-aqueous electrolyte solution on the surface of the positive electrode active material, and can improve the battery life. However, when the amount of the adhering quantity is too small, the effect is not sufficiently exhibited. If the amount is too large, the resistance may increase in order to inhibit the entry and exit of lithium ions.

[electrode]
As the binder for binding the active material, any material can be used as long as it is a material that is stable with respect to the solvent and the electrolyte used in manufacturing the electrode. For example, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyolefins such as polyethylene and polypropylene, polymers having unsaturated bonds such as styrene / butadiene rubber, isoprene rubber and butadiene rubber, ethylene-acrylic acid copolymers, An acrylic acid polymer such as an ethylene-methacrylic acid copolymer may be used.

The electrode may contain a thickener, a conductive material, a filler and the like in order to increase mechanical strength and electrical conductivity.
Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein.

Examples of the conductive material include metal materials such as copper and nickel, and carbon materials such as graphite and carbon black.
The electrode may be manufactured by a conventional method. For example, it can be formed by adding a binder, a thickener, a conductive material, a solvent or the like to a negative electrode or a positive electrode active material to form a slurry, applying the slurry to a current collector, drying it, and then pressing it.

In addition, a material obtained by adding a binder or a conductive material to an active material is roll-formed as it is to form a sheet electrode, a pellet electrode is formed by compression molding, and an electrode is formed on the current collector by techniques such as vapor deposition, sputtering, or plating. A thin film of material can also be formed.
When graphite is used as the negative electrode active material, the density of the negative electrode active material layer after drying and pressing is usually 1.45 g / cm ³ or more, preferably 1.55 g / cm ³ or more, more preferably 1.60 g. / Cm ³ or more, particularly preferably 1.65 g / cm ³ or more.

The density of the positive electrode active material layer after drying and pressing is usually 2.0 g / cm ³ or more, preferably 2.5 g / cm ³ or more, more preferably 3.0 g / cm ³ or more.
Various types of current collectors can be used, but metals and alloys are usually used. Examples of the current collector for the negative electrode include copper, nickel, and stainless steel, and copper is preferred. Examples of the positive electrode current collector include metals such as aluminum, titanium, and tantalum, and alloys thereof, and aluminum or an alloy thereof is preferable.

[Separator, exterior body]
A porous film (separator) is interposed between the positive electrode and the negative electrode to prevent a short circuit. In this case, the electrolytic solution is used by impregnating the porous membrane. The material and shape of the porous film are not particularly limited as long as it is stable to the electrolytic solution and excellent in liquid retention, and a porous sheet or nonwoven fabric made of a polyolefin such as polyethylene or polypropylene is preferable.
The material of the battery casing used in the battery according to the present invention is also arbitrary, and nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, a laminate film, or the like is used.
The operating voltage of the non-aqueous electrolyte secondary battery of the present invention described above is usually in the range of 2V to 6V.

[Action mechanism]
The reason why the nonaqueous electrolytic solution according to the present invention suppresses the initial efficiency, the low temperature discharge characteristics and the amount of gas generated during high temperature storage is not clear, and the present invention is not limited to the following mechanism of action. It is guessed as follows.
The fluorine-substituted ether represented by the chemical formula (I) is reduced on the negative electrode to form a stable protective film on the negative electrode surface, and suppresses side reactions of the electrolyte components, thereby increasing charge / discharge efficiency and storing at high temperature. It is thought that this has the effect of suppressing the amount of gas generated at the time. In addition, it is considered that the amount of gas generated during high-temperature storage is suppressed by setting the vapor pressure within an appropriate range. In addition, since the fluorine-substituted ether represented by the chemical formula (I) is excellent in compatibility with other solvents, it does not cause phase separation even at low temperatures or when the lithium ion concentration is changed, thereby improving discharge characteristics. it is conceivable that.

  Monofluorophosphate and difluorophosphate are considered to improve discharge characteristics by adsorbing on the positive electrode and assisting the movement of lithium ions. Monofluorophosphate and difluorophosphate are both composed of inorganic anions having similar ionic strength and ion volume, and are considered to exhibit the same effect. Moreover, since these salts produce an effect by the anion ionized in the electrolytic solution, it is considered that lithium ions can be similarly transferred on the positive electrode regardless of the type of the counter cation.

  In addition, the fluorine-containing ether represented by the chemical formula (I) and three or more cyclic carbonates including ethylene carbonate and a cyclic carbonate compound having a carbon-carbon unsaturated bond, and the volume of ethylene carbonate is another cyclic carbonate. By keeping the lithium ion concentration in a range that is less than the total amount, the amount of oxidative decomposition of ethylene carbonate on the positive electrode can be suppressed, so that the amount of high-temperature storage gas is suppressed it is conceivable that.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited to these Examples, unless the summary is exceeded.
In addition, each evaluation method of the battery obtained by the following Example and the comparative example is shown below.
[Initial efficiency evaluation]
A nonaqueous electrolyte secondary battery is charged to 4.1 V with a constant current corresponding to 0.2 C at 25 ° C. in a state of being pressed between glass plates, and then up to 3 V with a constant current of 0.2 C. Discharged. This was performed for 3 cycles to stabilize the battery. Next, after charging to 4.2 V with a constant current of 0.7 C, charging was performed until the current value reached 0.05 C with a constant voltage of 4.2 V, and the initial charge capacity was determined. Then, it discharged to 3V with the constant current of 0.2C, and calculated | required the initial stage discharge capacity. The ratio of the initial discharge capacity to the initial charge capacity was determined, and this was defined as the initial efficiency (%).
Here, 1C represents a current value for discharging the reference capacity of the battery in one hour, and for example, 0.2C represents a current value of 1/5 thereof.

[Low-temperature discharge characteristics evaluation test]
After completion of the initial capacity evaluation test, the battery was charged to 4.2 V with a constant current of 0.7 C at 25 ° C., and then charged to a current value of 0.05 C with a constant voltage of 4.2 V. Subsequently, it was cooled to −10 ° C. and discharged to 3 V at a constant current of 1 C, and the low temperature discharge capacity was determined. The ratio of the low-temperature discharge capacity to the initial discharge capacity was determined, and this was defined as the low-temperature discharge characteristic (%).

[Evaluation test of gas generated during high temperature storage]
After completion of the initial efficiency evaluation test, the battery was charged to 4.2 V at a constant current of 0.7 C at 25 ° C., and then charged to a current value of 0.05 C at a constant voltage of 4.2 V. Then, after immersing in an ethanol bath and measuring the volume, it was stored at 85 ° C. for 1 day.
The battery was cooled to 25 ° C. and then immersed in an ethanol bath to measure the volume, and the amount of gas generated from the volume change before and after storage was determined.

Example 1
<Preparation of non-aqueous electrolyte solution>
Under a dry argon atmosphere, ethylene carbonate (EC), butylene carbonate (BC), ethyl methyl carbonate (EMC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether ( A mixed solvent of A1) (capacity ratio 30: 10: 55: 5) was mixed with 0.5% by mass of lithium difluorophosphate (B1) as the content in the non-aqueous electrolyte, and then fully dried LiPF ₆ Was dissolved to a ratio of 1 mol / liter to prepare an electrolytic solution.

<Preparation of positive electrode>
An N-methylpyrrolidone solvent containing 94% by mass of lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material, 3% by mass of acetylene black as a conductive material, and 3% by mass of polyvinylidene fluoride (PVdF) as a binder The slurry was mixed with a disperser. This was uniformly applied on both sides of a 15 μm thick aluminum foil, dried, and then pressed so that the density of the positive electrode active material layer was 3.1 g / cm ³ to produce a positive electrode.

<Production of negative electrode>
Artificial graphite powder KS-44 (trade name, manufactured by Timcal Co., Ltd.) as a negative electrode active material, 98 parts by mass, an aqueous dispersion of sodium carboxymethylcellulose (concentration of 1% by mass of carboxymethylcellulose sodium) as a thickener and a binder, respectively, 100 mass And 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber 50% by weight) were added and mixed with a disperser to form a slurry. This slurry was uniformly applied to one side of a 10 μm thick copper foil, dried, and then pressed so that the density of the negative electrode active material layer was 1.6 g / cm ³ to prepare a negative electrode.

<Production of secondary battery>
The positive electrode, the negative electrode, and the polyethylene separator were laminated in the order of the positive electrode, the separator, the negative electrode, the separator, and the positive electrode to produce a battery element. After inserting this battery element into a bag made of a laminate film in which both surfaces of aluminum (thickness 40 μm) are coated with a resin layer while projecting positive and negative terminals, a non-aqueous electrolyte solution is injected into the bag, Vacuum sealing was performed to produce a sheet-like non-aqueous electrolyte secondary battery.
Using this non-aqueous electrolyte secondary battery, an initial efficiency evaluation test, a low temperature discharge characteristic evaluation test, and a generated gas amount evaluation test during high temperature storage were performed. The evaluation results are shown in Table 2.

(Examples 2 to 13, Comparative Examples 1 to 11)
An initial efficiency evaluation test, a low temperature discharge characteristic evaluation test, and a generated gas amount evaluation test during high temperature storage were carried out in the same manner as in Example 1 except that the nonaqueous electrolytic solution having the composition shown in Table 1 was used. The evaluation results are shown in Table 2.

Here, the symbols in Table 1 are as follows.
EC: ethylene carbonate VC: vinylene carbonate VEC: vinyl ethylene carbonate BC: butylene carbonate PC: propylene carbonate FEC: fluoroethylene carbonate A1: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoro Propyl ether (CF ₂ HCF ₂ CH ₂ OCF ₂ CF ₂ H)
A2: 1,1,2,2-tetrafluoroethyl-2,2,3,3,3-pentafluoropropyl ether (CF ₃ CF ₂ CH ₂ OCF ₂ CF ₂ H)
A3: Ethoxy-2,2,2-trifluoroethoxy-ethane (CF ₃ CH ₂ OCH ₂ CH ₂ OCH ₂ CH ₃ )
B1: Lithium difluorophosphate

From Table 2, comparison between Example 1 and Comparative Examples 1 and 2 improves initial efficiency and low-temperature discharge characteristics by simultaneously using a fluorine-substituted ether represented by chemical formula (I) and difluorophosphate. In addition, it can be seen that the amount of gas generated during high-temperature storage is suppressed.
Further, it contains three or more kinds of cyclic carbonates including a fluorine-substituted ether represented by chemical formula (I) and ethylene carbonate and a cyclic carbonate compound having a carbon-carbon unsaturated bond, and the volume of ethylene carbonate is another cyclic carbonate. It can be seen that the initial efficiency and the low-temperature discharge characteristics are improved and the amount of gas generated during high-temperature storage is suppressed by setting the amount to a range smaller than the total amount (Examples 2 and 6).
In addition, it can be seen that simultaneous use of difluorophosphate further improves the initial efficiency and low-temperature discharge characteristics, and suppresses the amount of gas generated during high-temperature storage (Examples 3 to 5, 7 to 9). .

[Compatibility test]
(Example 10)
Under a dry argon atmosphere, a mixed solvent (capacity) of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (A1) In a ratio of 30:50:20), fully dried LiPF ₆ was dissolved at a ratio of 1 mol / liter. When this electrolytic solution was visually confirmed at 25 ° C. and −10 ° C., no phase separation was observed.

(Example 11)
Mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3,3-pentafluoropropyl ether (A2) in a dry argon atmosphere In a volume ratio of 30:50:20, LiPF ₆ that was sufficiently dried was dissolved at a ratio of 1 mol / liter. When this electrolytic solution was visually confirmed at 25 ° C. and −10 ° C., no phase separation was observed.

(Example 12)
In a dry argon atmosphere, a mixture solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and ethoxy-2,2,2-trifluoroethoxy-ethane (A3) (volume ratio 30:50:20) Dry LiPF ₆ was dissolved at a rate of 1 mol / liter. When this electrolytic solution was visually confirmed at 25 ° C. and −10 ° C., no phase separation was observed.

(Comparative Example 3)
In a dry argon atmosphere, a well-dried LiPF ₆ in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and nonafluorobutyl ethyl ether (volume ratio 30:50:20) was 1 mol / liter. It dissolved so that it might become. When this electrolytic solution was visually confirmed at 25 ° C. and −10 ° C., phase separation was observed at any temperature.

  From comparison between Examples 10 to 13 and Comparative Example 3, it can be seen that the use of the fluorine-substituted ether represented by the chemical formula (I) improves the compatibility and increases the stability of the electrolytic solution.

  According to the present invention, it is possible to provide a non-aqueous electrolyte battery that is excellent in initial efficiency and low-temperature discharge characteristics and has a suppressed amount of gas generated during high-temperature storage.

Claims (7)

A non-aqueous electrolyte solution used in a non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution is represented by the chemical formula (I). A non-aqueous electrolytic solution containing a fluorine-substituted ether and a monofluorophosphate and / or difluorophosphate.

(In the formula, Rf ₁ represents a hydrogen atom, a fluorine atom, an alkyl group in which at least some of the hydrogen atoms are substituted with fluorine atoms, or an alkoxyalkyl group in which at least some of the hydrogen atoms are substituted with fluorine atoms. Rf ₂ represents an alkyl group in which at least some of the hydrogen atoms are substituted with fluorine atoms, excluding one hydrogen atom bonded to the terminal carbon atom, or alkoxy in which at least some of the hydrogen atoms are optionally substituted with fluorine atoms Represents an alkyl group.) In the chemical formula (I), Rf ₁ represents a hydrogen atom, a fluorine atom, a methyl group in which at least a part of hydrogen atoms are substituted with a fluorine atom, and Rf ₂ represents one hydrogen atom bonded to a terminal carbon atom. And an alkyl group having 1 to 3 carbon atoms in which at least a part of hydrogen atoms are substituted with fluorine atoms or an alkoxyalkyl group having 2 to 5 carbon atoms in which at least a part of hydrogen atoms may be substituted with fluorine. The non-aqueous electrolyte solution according to claim 1, wherein:   A non-aqueous electrolyte used for a non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte, and a fluorine-substituted ether represented by the chemical formula (I) A non-aqueous system comprising three or more cyclic carbonate compounds including ethylene carbonate and a cyclic carbonate compound having a carbon-carbon unsaturated bond, and the volume of ethylene carbonate is less than the total amount of the other cyclic carbonate compounds Electrolytic solution. In the chemical formula (I), Rf ₁ represents a hydrogen atom, a fluorine atom, a methyl group in which at least a part of hydrogen atoms are substituted with a fluorine atom, and Rf ₂ represents one hydrogen atom bonded to a terminal carbon atom. And an alkyl group having 1 to 3 carbon atoms in which at least a part of hydrogen atoms are substituted with fluorine atoms or an alkoxyalkyl group having 2 to 5 carbon atoms in which at least a part of hydrogen atoms may be substituted with fluorine. The non-aqueous electrolyte solution according to claim 3. 5. The non-aqueous electrolysis according to claim 3, comprising a cyclic carbonate represented by the chemical formula (II) as a cyclic carbonate compound other than ethylene carbonate and a cyclic carbonate compound having a carbon-carbon unsaturated bond. liquid.

(In the formula, R ₁ to R ₄ represent a hydrogen atom, a halogen atom, or a methyl group or an ethyl group in which the hydrogen atom may be substituted with a halogen atom.)   The nonaqueous electrolytic solution according to any one of claims 3 to 5, further comprising a monofluorophosphate and / or a difluorophosphate.   A nonaqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a nonaqueous electrolyte, wherein the nonaqueous electrolyte is the nonaqueous electrolyte according to any one of claims 1 to 6. A non-aqueous electrolyte secondary battery characterized by the above.